The invention relates to load balancing in packet switched telecommunications systems, and particularly to load balancing in telecommunications systems supporting Mobile IP (Internet Protocol).
During the past few years the mobility of employees has steadily been on the increase and nothing indicates that the trend would change. To connect a mobile node to an IP network poses a variety of problems, however. As a solution to this problem, the Mobile IP working group within the Internet Engineering Task Force (IETF) has defined an IP mobility protocol, i.e. Mobile IP protocol in specifications RFC2002 to RFC2004 and RFC2290. Reference is made to FIG. 1 which shows a telecommunications system supporting the Mobile IP protocol. Mobile IP is a mechanism for providing telecommunications features to a user of a mobile node by means of an IP address. It allows mobile nodes MN to change their access point to the Internet without changing their IP address. Thus, it facilitates the communication of the mobile node MN and a corresponding host CH communicating therewith with the home address of the mobile node MN.
Within the scope of the present application a “mobile node” MN refers to a host that wishes to use a home network HN address while being connected to any network other than the home network HN. For example, this may be point-to-point connecting by using e.g. telephone, ISDN or cellular connections or connecting through an access network that is connected to the Internet via a router, such as a wireless local area network (WLAN) hot spot. The “home network” HN is possibly a virtual IP network, to which the user of the mobile node MN logically belongs. In physical terms, it can be e.g. a local area network LAN which is connected to the Internet via a router. The “home address” is an address that is assigned for an extended period of time to a mobile node MN. It may remain unchanged regardless of where the mobile node MN is connected to the Internet. Alternatively, it can be assigned from an address pool. The “home agent” HA is a routing entity in the mobile node's MN home network HN which forwards packets by tunneling to the mobile node MN while this is away from the home network HN and maintains current location information of the mobile node MN. Tunneling refers to forming a virtual link, a tunnel, between the nodes.
If the mobile node MN, when being activated or moving, detects that it is in a visited network VN, it can register via a “foreign agent” FA with the home agent HA and Mobile IP functionality can be activated. The foreign agent FA refers to a routing entity in the mobile node's MN visited network VN which provides routing services to the mobile node NM while registered, and thus allows the mobile node MN to utilize its home network HN address. The foreign agent FA transmits to the mobile node MN packets tunneled by the home agent HA. For packets sent by the mobile node MN the foreign agent FA can serve as a default router of registered mobile nodes MN.
RFC2002 defines a care-of address COA as a termination point of a tunnel toward a mobile node MN for packets to be transmitted to a mobile node MN in a visited network VN. The mobile node MN can receive advertisement messages comprising COA from foreign agents FA. One foreign agent FA can produce more than one COA in its advertisement messages. The mobile node MN registers its COA with the home agent HA by sending a registration request. The home agent HA responds with a registration reply and maintains mobility binding for the mobile node MN. “Mobility binding” is the association of a home address with a care-of address COA, along with the remaining lifetime of that association. The mobile node MN may have a plurality of COAs simultaneously.
Scalability of the Mobile IP protocol is often doubted, in particular as regards the home agents. If an organisation administering the home network has a considerable number of mobile nodes, there have to be a plurality of home agents as well. By current methods, the mobile nodes have to be configured separately by the home agent, and consequently addition of home agents for load balancing requires manual updating. For instance, if it is noted that the installed home agents cannot cope with the load produced by the mobile nodes, a new home agent has to be installed in the network and some of the mobile nodes have to be configured to use the new home agent.